Effect of zirconia surface conditioning before glazing on the wear of opposing enamel: an in vitro study

OBJECTIVES

This in vitro study aimed to evaluate the wear of natural teeth opposing 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with different surface conditions.

MATERIALS AND METHODS

Sixty 3Y-TZP specimens were randomly assigned to six groups (n = 10), differing in surface condition. In three groups, the samples underwent glazing-with the glaze applied to roughened (i.e., 106-µm-grit diamond-finished), as-sintered, and polished zirconia. The three remaining groups consisted of unglazed specimens: solely polished samples and diamond-finished samples (106-µm-grit and 46-µm-grit) without further conditioning. Two-body wear was evaluated at extracted, non-carious molars (n = 60), which served as antagonists in chewing simulation (10,000 masticatory cycles, 49N load). As a control, natural teeth with intact enamel surfaces were tested against natural molars (n = 10). All samples were 3D-scanned before and after the chewing simulation (7 Series, Straumann). Volume loss was calculated (Inspect Software, GOM), and statistically analyzed (SPSS Statistics 24, IBM).

RESULTS

Volume loss of the natural antagonists decreased in the following order: 106-µm-grit diamond-finished zirconia (4.6 ± 2.5 mm3), glazed 106-µm-grit diamond-finished zirconia (3.8 ± 1.1 mm3), glazed as-sintered zirconia (3.5 ± 0.9 mm3), 46-µm-grit diamond-finished zirconia (1.7 ± 0.6 mm3), control (1.6 ± 0.7 mm3), glazed polished zirconia (1.4 ± 0.5 mm3), and solely polishing (0.4 ± 0.2 mm3). Even when polishing the surfaces before glazing, volume loss was not mitigated to the same extent as after polishing alone.

CONCLUSIONS

The zirconia surface condition beneath the glazing influences antagonist wear. Although polishing before glazing resulted in acceptable levels of antagonist wear, this approach did not yield as favorable results as polishing alone.

CLINICAL RELEVANCE

For operators favoring glazing, pre-polishing the zirconia surface could be advantageous to reduce wear.

Cleansing efficacy of an oral irrigator with microburst technology in orthodontic patients-a randomized-controlled crossover study

OBJECTIVES

Orthodontic patients struggle with interdental cleaning calling for simpler mechanical devices to reduce the high plaque levels. The present study aimed to compare the cleansing efficacy of an oral irrigator with that of dental flossing in patients with fixed braces after 4 weeks of home-use.

MATERIALS AND METHODS

The study design is a randomized and single-blinded cross-over study. After 28 days using the products at home, hygiene indices (Rustogi Modified Navy Plaque Index (RMNPI); gingival bleeding index (GBI)) were compared between test (oral irrigator) and control product (dental floss).

RESULTS

Seventeen adult individuals finalized the study. After 28 days of cleaning with the oral irrigator, RMNPI was 54.96% (46.91-66.05) compared to 52.98% (42.75-65.60) with dental floss (p = 0.029). Subgroup analysis revealed that the higher cleansing efficacy of the dental floss is attributable to buccal and marginal areas. GBI after the test phase with the oral irrigator was 12.96% (7.14-24.31) and statistically significantly higher compared to 8.33% (5.84-15.33) with dental floss (p = 0.030) which could be seen in all subgroups.

CONCLUSIONS

Oral irrigators do not remove plaque and reduce gingival bleeding as efficiently as dental floss in easily accessible regions. However, in posterior regions, where the patients struggled with the application of dental floss, the oral irrigator showed similar results.

CLINICAL RELEVANCE

Oral irrigators should only be recommended to orthodontic patients who cannot use interdental brushes and are not compliant with dental flossing.

Dentists' Working Conditions during the First COVID-19 Pandemic Lockdown: An Online Survey

The aim of this study was to investigate the operating conditions of dentists in Central Europe during the first coronavirus disease 2019 (COVID-19) lockdown. A survey including 24 questions was emailed to dentists in Austria, Germany, Switzerland and South Tyrol (Italy). Questions regarding dentists’ field of work, working hours, treatments performed, personal protective equipment and protocols, and economic consequences were asked. 1731 participants were included. 30.4% of participants worked mainly in Austria, 60.8% in Germany, 6% in Switzerland and 2.1% in South Tyrol. A country-specific analysis for the situation of South Tyrol was not possible due to the low participation; 53.7% of German, 45.5% of Austrian, and 11.7% of Swiss respondents reduced their working hours; 42.8% of Austrian, 41.5% of Swiss, and 17.3% of German participants closed their offices temporarily; 52.2% of respondents provided emergency service including pain management, restorations/temporaries, and denture repairs. A lack of access to FFP2/FFP3 (filtering facepiece) respirators was indicated by 59.4% Austrian, 38.0% German, and 11.7% Swiss dentists (p < 0.001). FFP2/FFP3 respirators were, when available, most frequently used in Austria (86.9%), followed by Switzerland (61.2%) and Germany (56.7%) (p < 0.001). Financial consequences could not be conclusively quantified by 58.6% of the participants. Most respondents in all partaking countries made use of governmental support. A lack of blueprints/guidelines resulted in heterogeneous working conditions. In consideration of a potentially high risk of infection in the dental setting, non-emergency dental treatments were largely suspended in all participating countries.

Cleansing efficacy of an auto-cleaning electronic toothbrushing device: a randomized-controlled crossover pilot study

Objectives

To compare the cleansing efficacy of a representative “ten seconds” auto-cleaning device with that of uninstructed manual toothbrushing in a pilot study.

Materials and methods

Twenty periodontally healthy probands refrained from oral hygiene for 3 days. Baseline full-mouth plaque scores (Rustogi Modified Navy Plaque Index, RMNPI) were assessed. After randomization, probands cleaned their teeth either with the auto-cleaning test device according to the manufacturer’s protocol or with a manual toothbrush. Plaque reduction was assessed by two aligned blinded investigators. After a 2-week recovery, the clinical investigation was repeated in a crossover design. The brushing pattern of the auto-cleaning device was analyzed in probands’ casts.

Results

Full-mouth plaque reduction was 11.37 ± 3.70% for the auto-cleaning device and 31.39 ± 5.27% for manual toothbrushing (p < 0.0001). The investigation of the auto-cleaning device’s brushing pattern in dental casts revealed a positive relationship of bristle rows in contact with tooth surfaces and the cleansing efficacy in the respective areas. A maximum of 2/4 bristle rows were in contact with the tooth surfaces; in some areas, the bristles had no contact to the teeth.

Conclusions

Uninstructed manual toothbrushing is superior to auto-cleaning. The alignment and density of the auto-cleaning device’s bristle rows need to be improved, and assorted sizes would be necessary to cover different jaw shapes.

Clinical relevance

The auto-cleaning device has been developed to accommodate individuals with poor dexterity or compliance. To date, it is unable to provide sufficient plaque reduction due to an inappropriate bristle alignment and poor fit with diverse dental arches.